1. Field of the Invention
The present invention relates to an exposure device and an exposure method.
2. Background Information
A stepper is employed as an exposure device, and serves to form circuit patterns on a semiconductor substrate (such as a silicon wafer and the like) in semiconductor devices, liquid crystal display devices, and the like. The stepper is a device that exposes a plurality of circuit patterns onto a substrate by projecting and repeatedly transferring a reduced version of a circuit pattern formed on a reticule onto the substrate via an optical projection system.
FIG. 9A is a schematic diagram of a conventional stepper used with silicon wafers, and FIG. 9B is an enlarged view of a support portion included in the stepper shown in FIG. 9A. The stepper shown in FIGS. 9A and 9B includes a condenser lens 2 that restricts the light from a light source 1, a reticule 3, an optical projection system 4, a position adjustment unit 5, and a wafer holder 12. A wafer 15 is mounted on the wafer holder 12. The light source 1, the condenser lens 2, the reticule 3, and the optical projection system 4 are sequentially disposed along an optical axis 17 of the light source 1 and perpendicular therewith. The reticule 3 includes a circuit pattern that will be formed on the wafer 15, and receives light from the condenser lens 2. The light that passes through the circuit pattern is projected at a reduced size onto the wafer 15 by means of the optical projection system 4, and is imaged onto the current shot region on the wafer 15.
The position adjustment unit 5 includes an X stage 6, a Y stage 7, a Z stage 8, a θ stage 9, and a leveling stage 10 that are disposed along the optical axis of the optical projections system 4, moves the wafer 15 by means of a motor drive, and positions the current shot region on the wafer 15 in the focal position of the optical projection system 4. Here, the X stage 6 moves the wafer 15 along the X axis of FIG. 9A that is in a plane perpendicular to the optical axis 17, the Y stage 7 moves the wafer 15 along the Y axis of FIG. 9A that is perpendicular to the optical axis 17 and the X axis, the Z stage 8 moves the wafer 15 along the Z axis of FIG. 9A that is parallel to the optical axis 17, and the θ stage 9 rotates the wafer 15 in a plane perpendicular to the optical axis 17. In addition, the leveling stage 10 includes three support portions 11a, 11b, and 11c. The lengths of the support portions 11a–11c are adjusted by means of the motor drive, and, as shown in FIGS. 10 and 11, thereby allow correction of any distortion of the subject image in the image plane (i.e., distortion of the circuit pattern) caused by warping/uneven surfaces located on the surface of the wafer 15 and/or any aberration or distortion in the condenser lens 2 or the lenses inside the optical projection system 4.
FIGS. 10A and 10B illustrate the operation of the leveling stage 10 and the support portions 11 in response to a warp/uneven surface located on the wafer 15. In FIG. 10A, the image plane A from the optical projection system 4 and the exposure surface of the wafer 15 do not match because there is a warp/uneven surfaces located on the wafer 15. Accordingly, as shown in FIG. 10B, the lengths of the support portions 11a–11c on the leveling stage 10 are adjusted to tilt the wafer holder 12 and the wafer 15 so that the image plane A and the exposure surface of the wafer 15 will match.
In addition, FIGS. 11A and 11B illustrate the operation of the leveling stage 10 and the support portions 111 in response to distortion of the subject image in the image plane A caused by an aberration or distortion in one or more of the lenses of the stepper. In FIG. 11A, the image plane A and the exposure surface of the wafer 15 do not match, thereby producing a distortion in the subject image on the exposure surface. Accordingly, as shown in FIG. 11B, the lengths of the support portions 11a–11c on the leveling stage 10 are adjusted to tilt the wafer holder 12 and the wafer 15 so that the image plane A and the exposure surface of the wafer 15 will match.
However, with the stepper disclosed in FIGS. 9A and 9B, the speed at which the lengths of the support portions 11a–11c on the leveling stage 10 are adjusted by the motor drive is slow. Thus, it will take time to correct any distortion of the subject image in the image plane caused by warping/uneven surfaces located on the wafer 15 and/or aberration or distortion in one or more of the lenses, and thus the time needed for the entire exposure process will increase. In addition, electric power consumption costs will increase because the support portions 11a–11c are operated by the motor drive.
Furthermore, it is difficult to perform localized corrections because tilting on the wafer 15 is corrected by adjusting the tilt of the wafer holder 12 by means of the support portions 11a–11c. In addition, even if warping/uneven surfaces located on the wafer 15 and/or aberration or distortion in the lenses is localized, the operational range of the support portions 11a–11c will increase because it will be necessary to adjust the tilting on the entire wafer 15 by means of the support portions 11a–11c. Thus, there will be a large amount of waste with respect to the amount of time the support portions 11a–11c are driven and the amount of electric power consumed therefor. Furthermore, warping/uneven surfaces on the wafer 15 caused by the presence of a foreign substance between the wafer holder 12 and the rear surface of the wafer 15 cannot be corrected by adjusting the tilt of the wafer holder 12.
In view of the above, there exists a need for an exposure device and an exposure method which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.